The use of ambient light to power a low power demand device has been approached in several ways. One method utilizes a large photovoltaic array approximately 16 cm.sup.2 to charge batteries. Another approach uses no batteries, but requires a similarly large array area to provide sufficient electric power, on the order of 10 cm.sup.2 of photovoltaic cells.
A compounding problem exists in an office or home environment where the light levels are lower than those which are found outdoors in direct sunlight. This requires a large surface area to be exposed to the lower lighting levels, or an increase in efficiency of the power converting cells.
One method proposed to increase efficiency utilizes a planar luminescent greenhouse collector. See: J. A. Levitt and W. H. Weber, Applied Optics, Vol. 16, No. 10, October 1977. A solid sheet of glass or plastic is infused with a luminescent dye. When the dye is exposed to light, the dye re-emits a particular frequency of light. This light is trapped within the solid by polished surfaces of the solid. Photovoltaic cells are optically coupled to faces and are designed to be particularly responsive to the light frequency emitted by the dye. Thus, the effect is a collection of the ambient light, and a concentration of the light at the desired wavelength for maximum conversion into electric power. This procedure, however, still does not attain the efficiency levels required for a small collector surface area coupled with a low light level such as is found in an office environment.
Accordingly, an object of the present invention is to increase the light collector efficiency to the point that an electronic device such as a calculator can be powered by a small surface area collector, without batteries, and be operable in a low light environment such as an office, while requiring 1.3 cm.sup.2 of photovoltaic area or less, and thus reduce costs considerably.